Ge surface cleaning B. Majorowits a , M. Wojcik b , G. Zuzel b ) - - PowerPoint PPT Presentation

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Ge surface cleaning B. Majorowits a , M. Wojcik b , G. Zuzel b ) - - PowerPoint PPT Presentation

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Ge surface cleaning B. Majorowits a , M. Wojcik b , G. Zuzel b ) MPI-P , Munich a ) IF UJ, Krakow b GERDA general meeting, LNGS Italy, 1-3.03.2010 Outlook Applied technique for Ge cleaning - Loading samples with the Rn daughters -

slide-1
SLIDE 1

GERDA general meeting, LNGS Italy, 1-3.03.2010

Ge surface cleaning

  • B. Majorowitsa, M. Wojcikb, G. Zuzelb

a ) MPI-P

, Munich

b ) IF UJ, Krakow

slide-2
SLIDE 2

GERDA general meeting, LNGS Italy, 1-3.03.2010

Outlook

 Applied technique for Ge cleaning

  • Loading samples with the Rn daughters
  • Investigations of 210Pb/210Bi/210Po

 Ge surface treatment

  • Optical quality Ge
  • HPGe
  • Comparison with Copper and Steel

 Summary

slide-3
SLIDE 3

GERDA general meeting, LNGS Italy, 1-3.03.2010

Loading the samples

222Rn

source (1.4 MBq)

Pump

Filter Discs

slide-4
SLIDE 4

GERDA general meeting, LNGS Italy, 1-3.03.2010

Measuring 2

1 0 Pb/2 1 0 Bi/2 1 0 Po

Screening of 210Po with an alpha spectrometer 50 mm Si-detector, bcg ~ 2 α/d (1-10 MeV) sensitivity ~ 20 mBq/m2 (100 mBq/kg, 210Po)

Screening of 210Bi with a beta spectrometer 2×50 mm Si(Li)-detectors, bcg ~ 0.18/0.40 cpm sensitivity ~ 10 Bq/kg (210Bi)

Screening of 210Pb (46.6 keV line) with a gamma spectrometer 16 % - HPGe detector with an active and a passive shield

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SLIDE 5

GERDA general meeting, LNGS Italy, 1-3.03.2010

Optical quality Germanium

“Test run” before using HPGe

Samples cut out from bigger Ge pieces, no special surface treatment after cutting

2 discs 50 mm in diameter and 3 mm thick were exposed for 7 months to our Rn source (1.4 MBq)

Discs etched by Canberra according to their standard procedure applied to HPGe crystals

Discs before/after etching were screened for

210Pb/210Bi/210Pb

slide-6
SLIDE 6

GERDA general meeting, LNGS Italy, 1-3.03.2010

Optical quality Germanium - results

Isotope Disc side Initial activity [cpm] Activity after cleaning [cpm] Reduction factor R Average reduction factor Ra

v

Remarks

2 1 0 Pb

a 2.08 < 0.02 > 104 > 104

Amount of removed Ge not

  • measured. After etching side

b not measured for 2

1 0 Pb.

b 3.43

  • 2

1 0 Bi

a 42.7 < 0.18 > 237 > 427 b 67.9 < 0.11 > 617

2 1 0 Po

a 42.4 0.04 1060 2300 b 71.7 0.02 3585 Disc No. 1

slide-7
SLIDE 7

GERDA general meeting, LNGS Italy, 1-3.03.2010

Optical quality Germanium - results

Disc No. 2

Isotope Disc side Initial activity [cpm] Activity after cleaning [cpm] Reduction factor R Average reduction factor Ra

v

Remarks

2 1 0 Pb

a 2.09

  • > 106

Amount of removed Ge not

  • measured. After etching side

a not measured for 2

1 0 Pb. 2 1 0 Bi

not measured because it has decayed.

b 2.12 < 0.02 > 106

2 1 0 Bi

a 40.7

  • b

46.1

  • 2

1 0 Po

a 50.0 0.06 820 880 b 47.0 0.05 940 Activities of all isotopes reduced significantly after etching,

2 1 0 Po removed most efficiently

slide-8
SLIDE 8

GERDA general meeting, LNGS Italy, 1-3.03.2010

HPGe

 Two 50 mm in diameter and 3 mm

thick HPGe discs provided by MPI-M

 One disc and HP water (2 L) exposed

to the strong Rn source for 9 months

 Exposed disc etched by Canberra in

their standard solution, clean disc etched in a solution made with the exposed water

 Discs before/after etching screened for

210Pb/210Bi/210Pb

slide-9
SLIDE 9

GERDA general meeting, LNGS Italy, 1-3.03.2010

HPGe discs loading

222Rn

source (1.4 MBq)

Pump

Ge discs

Filter

HP Water Drying column (Si-Geel)

slide-10
SLIDE 10

GERDA general meeting, LNGS Italy, 1-3.03.2010

HPGe results

2 1 0 Po 2 1 0 Bi 2 1 0 Pb

Before cleaning 11.88 ± 0.19 14.70 ± 0.12 0.717 ± 0.011 After cleaning 0.102 ± 0.006 0.017 ± 0.008 < 0.001 Reduction factor 117 ± 7 865 ± 407 > 717

Exposed disc

2 1 0 Po 2 1 0 Bi 2 1 0 Pb

Before etching (background) 0.064 ± 0.005 0.111 ± 0.004 0.0163 ± 0.0004 After etching (average act. from both disc sides) bcg corrected! 0.023 ± 0.007 0.106 ± 0.011 0.0066 ± 0.0016 Increase above the background ~ 35 % ~ 100 % ~ 40 %

Unexposed disc Exposed water measured with an HPGe spectrometer did not show any activity above the background (LLL in HD).

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SLIDE 11

GERDA general meeting, LNGS Italy, 1-3.03.2010

Comparison between Cu/Steel/Ge

Isotope Average reduction factors for etching Copper Steel Ge (Opt. – HP)

2 1 0 Pb

~ 50 ~ 100 100 – 700

2 1 0 Bi

~ 50 ~ 100 400 – 800

2 1 0 Po

~ 1 ~ 20 1000 – 100

Etching of Copper is the less effective, for Po there is no effect

Results for Steel are acceptable, also Po has been removed

Etching of Ge is the most efficient, surface quality seems to play a role

slide-12
SLIDE 12

GERDA general meeting, LNGS Italy, 1-3.03.2010

Summary

Etching of opt. Ge/HPGe removes efficiently all long-lived Rn daughters

Small quantities of

210Pb/210Bi/210Pb found on the

surface of the unexposed disc etched in the contaminated solution (the level

  • f

water contamination was unknown) - for each sample a fresh solution is required in order to avoid re- depositon

210Po removed more efficient form optical quality

Ge, 210Pb/210Bi from HPGe – surface quality plays a role

Etching effectiveness in

210Pb/210Bi/210Po removal

differs for each isotope and for different materials (Cu, Steel, Ge)